1. Field of the Invention
The present invention relates to throwaway inserts (the term xe2x80x9cinsertxe2x80x9d hereinafter referred to represents a throwaway insert) to be used for cutting by being mounted to throwaway-type cutters such as end mills. The present invention also relates to throwaway-type cutters having the throwaway inserts mounted thereto.
2. Description of the Related Art
Hitherto, a milling machine, which is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 11-226812, has been known as a rotating tool used for cutting, such as plunging-milling and three-dimensional cutting. The milling machine is mounted with substantially rhombic-planar-shaped throwaway-inserts. A cutting edge used as a peripheral cutting edge when the throwaway insert is mounted to a tool part is provided with a sub-cutting-edge at a corner of the throwaway insert, the sub-cutting-edge being disposed in parallel to the rotational axis of the tool part. The cutting edge of the throwaway insert, which serves as a facing cutting edge when the throwaway insert is mounted to the tool part, has a sub-cutting-edge angle of 0.5 to 10 degrees.
Therefore, when the milling machine is transferred vertically so as to be used for plunging-milling, finish-machining can be performed by using the sub-cutting-edge of the peripheral cutting edge. however, when the milling machine is transferred horizontally, finish-machining cannot be performed because the facing cutting edge has the sub-cutting-edge angle; therefore, the insert must be replaced by another insert for finishing. Because of the same reason, there is a problem in that the insert, which is used in a right-hand tool part, cannot be used in a left-hand tool part.
There is another problem in that since the insert has a substantially planar shape, when the insert is mounted to a tool part so as to have a negative radial rake angle, the sharpness of the cutting edge is reduced and cutting resistance is increased although the thickness of a back metal part of an insert-mounting base can be designed to be large.
Accordingly, it is an object of the present invention to provide a throwaway insert which can be used for plunging-milling and transverse cutting and for finish-cutting, and a throwaway-type cutter using the throwaway insert.
To these ends, according to an aspect of the present invention, a throwaway insert comprises a pair of cutting edges merging with each other at a nose part of an upper face opposite to a mounting face. The pair of cutting edges are individually formed inclined so as to be closer to the mounting face from the nose part toward portions of the respective cutting edges apart from the nose part and individually include sub-cutting-edges in the vicinity of the nose part. The sub-cutting-edges form a substantially right angle therebetween.
Since the pair of cutting edges individually include the sub-cutting-edges in the vicinity of the nose part, which are disposed substantially perpendicular to each other, the sub-cutting-edge of the peripheral cutting edge and the sub-cutting-edge of the facing cutting edge function as finish-cutting edges when plunging-milling and traverse cutting, respectively, whereby finish-cutting such as finish-machining and medium-rough-finish-machining can be performed other than rough cutting. By individually providing the sub-cutting-edges at both sides of the nose part, a cutting insert regardless of handling can be obtained which can be mounted to either a right-hand tool part or a left-hand tool part. Since each cutting edge of the cutting insert is inclined with respect to the mounting face of the insert at which the insert is mounted to a tool part, the radial rake angle of the cutting edge is set, when mounted, so that the inner side end of the cutting edge is offset toward the trailing side of the rotation of the tool part with respect to the outer side end of the cutting edge, whereby sharpness of the cutting edge can be improved and cutting resistance can be reduced.
The sub-cutting-edges may be individually formed substantially in straight lines.
With the sub-cutting-edges thus formed, superior finish machining and medium-rough-finish machining can be performed.
The pair of cutting edges may be individually formed in a convex-curved shape. The cutting edges may be also convex-curve-shaped in a horizontal direction.
By forming the cutting edges in a convex-curved shape, the impact against the cutting edges when the cutting edges cut into a workpiece can be reduced. When the depth of cut is small, the cutting edge cuts into the workpiece at the end of the nose part, and when the depth of cut is large, the cutting edge cuts into the workpiece at an inner part of the cutting edge. Cut regions gradually expand from the cut-in points, whereby the impact on the cutting edge can be reduced and damages to the cutting edge can be suppressed.
The pair of cutting edges may form an acute angle of smaller than ninety degrees, for example, eighty degrees therebetween at the respective portions continuing from the sub-cutting-edges.
The throwaway insert may be formed in a substantially quadrilateral-planar shape, a pair of the nose parts of the upper face may be individually provided at corners, opposite to each other, of the substantially quadrilateral-planar throwaway insert, and rake faces on the upper face may be individually formed inclined so that the distances of the rake faces to a lower face individually decrease from the nose parts toward a diagonal line between a pair of the remaining corners of the substantially quadrilateral-planar throwaway insert.
Cut chips produced by the peripheral cutting edge and facing cutting edge are guided along the upper face to a portion along the diagonal line, and are curled and broken. The broken chips are discharged to the tool-part base-end side along the upper face along the diagonal line.
A throwaway-type cutter according to the present invention comprises a throwaway insert having the above-described configuration. The throwaway insert is mounted so that the nose part is positioned at the periphery of an end of a tool part. One of the pair of cutting edges serves as a peripheral cutting edge, the sub-cutting-edge of the one of the pair of cutting edges being disposed substantially in parallel to an axis of the tool part, and the other one of the pair of cutting edges serves as a facing cutting edge, the sub-cutting-edge of the other one of the pair of cutting edges being disposed substantially perpendicular to the axis of the tool part.
With this arrangement, the sub-cutting-edge of the peripheral cutting edge and the sub-cutting-edge of the facing cutting edge function as finish-cutting edges when plunging-milling and traverse cutting, respectively, whereby finish-cutting such as finish-machining and medium-rough-finish-machining can be performed other than rough cutting. By individually providing the sub-cutting-edges at both sides of the nose part, a cutting insert regardless of handling can be obtained which can be mounted to either a right-hand tool part or a left-hand tool part. Since each cutting edge of the cutting insert is formed inclined with respect to the mounting face of the insert at which the insert is mounted to a tool part, the radial rake angle of the cutting edge is set, when mounted, so that the inner side end of the cutting edge is offset toward the trailing side of the rotation of the tool part with respect to the outer side end of the cutting edge, whereby sharpness of the cutting edge can be improved and cutting resistance can be reduced.
In the throwaway-type cutter according to the present invention, the throwaway insert may be mounted in an insert pocket of the tool part in a manner such that a surface disposed in a region at a tool-part base-end side of the throwaway insert mounted in the insert pocket is inclined to the mounting face of the throwaway insert (to the trailing side of the rotation of the tool part) from the inner side of the tool part toward the outer side thereof.
The cut chips transferred to the base end side of the throwaway insert, when cutting, are guided along the inclined surface toward the peripheral side and are discharged to the outside.
A surface of the insert pocket may be inclined to the mounting face side of the throwaway insert (to the trailing side of the rotation of the tool part) from the inner side of the tool part toward the outer side thereof along a ridgeline opposite to the facing cutting edge of the throwaway insert.
The cut chips moving along the rake face of the upper face of the insert and transferred toward the base end side are smoothly transferred to the inclined surface of the insert pocket, and are discharged toward the base end side from the inclined surface.